The present invention relates generally to an optical filter, and more particularly to an electrically variable optical filter.
Many types of modern electronic devices use light waves in operation. Examples are imaging devices, measurement equipment, optical communications, optical computing, etc. During operation, such a device may filter or block incident light. For example, an electronic device may need to filter out specific wavelengths or bands of light.
In the prior art, filtering out of specific wavelengths or bands of light has been performed in many ways. The most common approach has been using mechanical devices, including tints, gratings, polarizers, etc., to provide a filter having a fixed wavelength transmission property.
Although prior art filters of fixed wavelength transmission properties are generally accurate and transmit a reasonable percentage of desired light, they lack an ability to accommodate changes in desired optical wavelengths.
In a growing number of applications there is a need for a variable optical filter. Prior art variable optical filters exist. In order to vary the filtered output wavelengths, the prior art approaches typically rely on multiple filters, mechanical filter selection, movable mirrors, etc. The prior art controllable filters therefore are mainly controllable in a mechanical fashion. However, such mechanical devices are vulnerable to dirt and wear, have a less than desired reliability, etc. Moreover, in prior art mechanically variable optical filter devices, the changing of the filter wavelength may suffer from an inadequate response time and may lack an adequate variable wavelength range. In addition, the prior art variable optical filters tend to be expensive and bulky.
Alternatively, prior art electrically variable optical filters exist. One example is an electrically controllable polarizer. Another prior art electrically variable optical filter uses a presence or absence of a fluid in a sealed channel to enable and disable filtering. Electrically controllable optical filters therefore generally comprise only an on/off control over the desired wavelength or band of light and cannot control the wavelength characteristics of the filter over a tunable band. For example, the wavelength in a sealed channel/fluid optical filter is not changeable due to the sealed nature of the channel.
Therefore, there remains a need in the art for improvements to optical filters.
An electrically variable optical filter comprises a first optical element including a first angled face and a second optical element including a second angled face. The second angled face is substantially parallel to and spaced apart from the first angled face. At least one separation actuator is affixed between the first optical element and the second optical element and is operable to change a separation distance D between the first angled face and the second angled face. Light waves transmitted through the first optical element are selectively transmitted through to or reflected away from the second optical element as a function of wavelength and the separation distance D.